1. Field of the Invention
The present invention relates to a power supply circuit for powering a traveling-wave tube.
2. Description of the Related Art
A traveling-wave tube must be supplied with a variety of voltages such as a heater voltage, a cathode voltage, a helix voltage, and a collector voltage. In addition, the respective voltages are sequentially applied in accordance with a predetermined procedure called an “anode sequence” in order to prevent excessive currents. After a heater has been sufficiently heated by the heater voltage applied thereto (for example, in several minutes), the helix voltage is applied. Then, according to the anode sequence, the anode voltage is applied later than the helix voltage.
For powering a traveling-wave tube in accordance with an anode sequence as mentioned above, a circuit including a relay has been conventionally required, and power supply apparatuses for traveling-wave tubes have been used in a variety of configurations (for example, see JP-11-149880-A).
FIG. 1 is a block diagram illustrating an exemplary configuration of a conventional power supply apparatus for traveling-wave tube. Referring to FIG. 1, conventional power supply apparatus 90 for a traveling-wave tube comprises collector power supply 91, helix power supply 92, heater power supply 93, and anode power supply 94. Anode power supply 94 includes resistors 95, 98, control circuit 96, and relay 97.
One electrode is commonly used as a heater electrode and a cathode electrode on the positive side of traveling-wave tube 99, so that this electrode is hereinafter called the “heater/cathode electrode.” Also, a heater electrode on the negative side of traveling-wave tube 99 is simply called the “heater electrode.”
Heater power supply 93 supplies a heater voltage between the heater/cathode electrode and heater electrode of traveling-wave tube 99. Collector power supply 91 supplies a collector voltage between a collector electrode and the heater/cathode electrode of traveling-wave tube 99. Helix power supply 92 supplies a helix voltage between a helix electrode and the heater/cathode electrode of traveling-wave tube 99.
Anode power supply 94 comprises control circuit 96 and resistor 95 connected in series between the helix electrode and heater/cathode electrode of traveling-wave tube 99; resistor 98 connected between the anode electrode and heater/cathode electrode; and relay 97 through which a junction between control circuit 96 and resistor 95 is connected to the anode electrode. Anode power supply 94 generates an anode voltage based on the helix voltage, and supplies the anode voltage between the anode electrode and heater/cathode electrode of traveling-wave tube 99.
Control circuit 96 includes a series regulator (not shown) for decreasing and stabilizing the helix voltage, and for setting a voltage at the junction between control circuit 96 and resistor 95 to the anode voltage or a voltage equal to or lower than a maximum open/close voltage of relay 97.
In this way, the conventional power supply apparatus for a traveling-wave tube detects a rising and a falling edge of the helix voltage to control on/off of the anode voltage through predetermined processing. The conventional power supply apparatus for a traveling-wave tube relies on this control to apply the anode voltage later than the helix voltage in accordance with the anode sequence to prevent an excessive current from flowing into the traveling-wave tube through the helix electrode.
However, the foregoing conventional power supply apparatus implies the following problems.
Power supply apparatus 90 for a traveling-wave tube illustrated in FIG. 1 requires control circuit 96 for detecting the helix voltage and performing the predetermined processing, and also requires a relay driving power supply (not shown) for driving relay 97. Also, isolation must be provided by a vacuum relay or the like between control circuit 96 which operates at a lower voltage and relay 97 which operates at a higher voltage. Thus, the conventional power supply apparatus for a traveling-wave tube is disadvantageously increased in size and cost. Also, since relays are generally prone to destruction due to vibrations and impacts, the power supply apparatus for a traveling-wave tube is disadvantageously vulnerable to vibrations and impacts.